The Role of Nitrate in Human Health

The enrichment of the biosphere with reactive nitrogen from anthropogenic origin, in combination with increased consumption of vegetables and (preserved) animal products, has led to increased intake by humans of nitrite and nitrate. Nitrate and nitrate-forming salts are among the key components of fertilizers and the increased dependency of farming practices on such fertilizers over several decades has led to increasing levels of human exposure. This arises from consumption of crops and from nitrate-contaminated drinking water due to agricultural land runoff For years, people have viewed dietary sources of nitrate as harmful to humans causing methemoglobinemia and cancers. However, methemoglobinemia is rare and evidence suggests a relation with infective enteritis rather than with nitrate alone. Also, epidemiological evidence for an association between cancers of the digestive tract and nitrate intake is inconclusive in terms of increased risks of cancer although the International Agency for Research on Cancer concluded "ingested nitrite or nitrate under conditions that result in endogenous nitrosation is probably carcinogenic to humans (Group 2A)". The discovery of the nitric oxide pathway in the early 1980s revealed that nitrate is produced endogenously in the body changing our perception of nitrate safety. Recently benefits of dietary sources of nitrate for cardiovascular health and protection against infections have been unveiled, calling for an assessment of the risk and benefits associated with nitrate in our food and water supply. The scope of this article is to review the current state of the science on nitrate in human health and disease.